Entangling the Enemy: Ecological, Systematic, and Medical Implications of Dermestid Beetle Hastisetae

SIMPLE SUMMARY: Larvae of Dermestidae Megatominae possess modified setae, called hastisetae, that serve as the primary defense against predators. These setae, beside a possible usage as discriminant character in larvae identification, are important contaminants of stored products, work and living environments. Exposure to hastisetae causes allergic reactions in humans and the insurgence of skin rashes, asthma, conjunctivitis, and digestive system inflammation. Very little is known about their mechanism of action, because the mechanical trap and their capability to penetrate throughout vertebrate epithelia remain unclear. The primary aim of the present contribution is to increase the general knowledge about hastisetae, exploring their diversity and fine morphology among genera and species. The insertion on integument, the pedicel, the shaft, and the apical head are illustrated in detail, and the first observation of active defensive behavior based on hastisetae is recorded and presented. The internal structure and the apex of the hastisetae are characterized for the first time, offering new interpretations in the action of hastisetae against vertebrates. Furthermore, possible implications to the systematics of skin beetles are proposed based on the results of the study. ABSTRACT: Hastisetae are modified setae typical of Dermestidae Megatominae and are a primary defensive tool of both larvae and pupae against invertebrates and possibly vertebrates. Given their unique morphological features, hastisetae have recently been suggested as an additional character useful for larvae identification and possible source of information to clarify the systematics of Megatominae. Hastisetae are also recognized as important contaminants of stored products, work and living environment; in particular, the exposure to hastisetae seems to cause allergic reactions and the insurgence of skin rashes, asthma, conjunctivitis, and digestive system inflammation in humans. Starting from these basic concepts, the present paper provides a detailed description of the hastisetae of some Megatominae. Fine morphology of external and internal microstructures of the hastisetae is shown and compared at the genus level. The insertion on integument, the pedicel, the shaft, and the apical head are illustrated in detail, and the first observations of active defensive behavior based on hastisetae are recorded and presented. Possible implications to the systematics of skin beetles are proposed based on the results of the study.